Motorsports Village

on a typical 23* sbc what would you consider the max difference in flow going from 28"to 38-40" before it would become a choke problem or hp loss, thanks-tom

You might want to read this thread on ST - http://speedtalk.com/forum/viewtopic.php?f=1&t=600 - where I was porting a set of Bowties for a friend. The heads flowed 275-280cfm when I was done and converted back very closely from 40". I recall them being within a couple cfm converted. I think the main thing is the flow curve should look the same at 28" and 40". On those bowtie heads the flow curve looked fine at 28" but dropped off at high lift at 40". You could hear it.

I'll type more tomorrow.

Rick

Several things to look for.

* When flowing at higher depressions you normally need to flow on a higher range. The port should flow the same on different ranges where they can overlap. If not you can get error there. Make sure your bench ranges correlate with each other.

* Make sure to use the slight range correction for the difference in test depression. I think I posted that before I think it changed my 351 range to a 347 range or something like that.

* If you have a difference between 40" flow (converted to 28") and 28" flow at low lifts it is unlikely to be a flow separation issue that can cause HP loss. It would more likely be a measurement error and that same % of difference would probably stay the same as lift goes up. So if they match at .300" lift within 2cfm then I'd expect them to be within 4cfm at .700" lift.

* If the flow gains or stays flat, when testing at 28", as the valve opens to full lift or a bit more then the flow should gain or stay flat thru the same lift range when testing at 40" or more. The lift/flow curve should look the same.


Those bowtie heads from that ST thread are still on a engine. The heads flowed about 280@28" (205cc), which was very small gain, when I got done but gained a lot at 40" from before the extra work. The SSR was a better shape. The engine pulled higher as well as more power at lower rpm. The mid-lift flow was hurt during that work. It ran .1-.2 better at the time. He ran a 6.11@112 weighing 2900# (DA=700). They are on a 383 with the same basic parts from that ST thread except a 383 now instead of 355 and it has a 1050 adapted to the v-jr.

Those heads showed within a couple cfm when converting from 40". I don't know that there is a fixed number to go by, the other things mentioned above are more important imo.

This is how I believe it is, but I don't have near enough information/data to say it's fact.

Rick

thanks, rick, i have to check the complete curve and figure the actual range difference by math, i guess i was looking for the easy answer too like within 7cfm , no hp loss over 8 cfm fix it, thanks again- tom

Easy and understanding the internal combustion engine don't seem to go together.

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Slow racing is better than no racing!

Randy

ha, yea i hear ya, a momentary laps of laziness in this steep uphill battle called airflow study

This is kinda related I think, so I hope Tom don't mind me asking on his thread.

How many have tested for stalling at a lower lift, when flowed at a higher depression?

On all of the ports I've tested, so far none have stalled at a lower lift when tested at a higher depression.

The idea sounds valid that if speed is the cause of stalling, it would stall sooner at higher depressions. I realise the running engine will pull higher depressions than we can on the flow bench, but wouldn't the trend be there if the depression is increased from 28" to 40"?

I mean if a port stalls at .600" lift when flowed at 28", wouldn't it at least stall at .575" at 40" if increased depression will cause it to stall sooner?

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Slow racing is better than no racing!

Randy

Dont want to hijak the thread,,,,but what are you guys seeing for flow loss on 23deg chev heads when bolting the manifold on??

And when using the flow number to calc HP

Like 280cfm@28 x.598 x.43 x8=576HP

but when you bolt intake on and it now only flows 262cfm@28(539HP)

Depends on the manifold & how well the head is done. IE; are all the entry angles done to match the intake's angles. I've seen several well designed sheetmetal manifolds make the flow numbers go up. You % losss is not real bad.

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www.adgersperf.com

Adger
After I saw your picture in the Magazine on EMC, I thought I wus the ugliest on here but now I am not sure . HeHeHe.
Hey how did the flowmasters work on the dynos(Hp loss?).
reed

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Grant's Custom & Racing Auto

Well, I'm glad there are two of us butt ugly guys in the world. I think they took that picture with a REAL Long lenses. I never saw what was going on.
Well, I'm not in the dyno dept. That is Wesley's area. They might loose HP, but they do help put on the program.
hope you have a Merry Christmas and i hope I can return the kind words, someday. TEHE!!!

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www.adgersperf.com

Damn, must have been a hell of a looong lense. HeHe. I still having problem with my neighbor on noise.
racear

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Grant's Custom & Racing Auto